抑制癌細胞的轉移一直是最主要的癌症治療重點，癌症轉移的相關機制在近年來也就逐漸成為癌症研究的目標。而對於癌症轉移的研究經常是在探討tumor progression (癌化)這個特殊的過程，意指腫瘤開始呈現侵犯性成長並有機會經由血液或淋巴系統擴散或轉移（metastasis）到身體其他區域，而在新的位置繼續形成新的腫瘤細胞。近年來，有許多科學家發現EMT 這個現象可以作為tumor progression(癌化)過程的正向指標。EMT (Epithelial-mesenchymal transition)是指從上皮細胞型態(epithelium)轉變成間葉細胞mesenchyme)型態的一種特殊過程，最初被定義為胚胎時期與器官發育現象相關，而近年來有許多文獻指出，EMT 參與癌細胞自良性腫瘤變成轉移性癌細胞的過程，被視為主要的癌化指標之一。真核核糖體蛋白P0 是真核生物中核糖體stalk 結構中非常重要的成分之ㄧ，除了在真核生物蛋白質合成的轉譯過程中，扮演絕對重要的角色之外，近年來被發現P0 蛋白在大腸癌、肝癌以及乳癌中有過度表現的情形。在實驗室先前的研究發現，P0 蛋白和Grap2 and cyclin D interacting protein (GCIP)有很強的交互作用，同時將P0 過度表現於人類乳癌及肝癌細胞後會使得細胞增生能力提升，顯示P0 應具有和腫瘤生成有關的功能。GCIP 全名為Grap2 and cyclin D interacting protein，在我們先前的研究中指出GCIP 蛋白表現量和乳癌和肝癌細胞癌化程度呈現負相關，同時也發現P0 和其交互作用的GCIP 蛋白會分別影響腫瘤生成及抑制的功能。我們推測P0 和其交互作用的GCIP 蛋白在細胞癌化的過程當中皆為重要的調節因子，因此藉由過度表現P0 和GCIP 蛋白的方式進一步觀察EMT 現象的產生是否有何改變。實驗結果發現過度表現P0 的前期乳癌細胞MCF-7 中，調控cell adhesion 及維持表皮細胞正常型態的重要因子E-Cadherin表現量明顯下降，同時伴隨其上游的轉錄因子Snail1 表現量上升，顯示癌細胞較有能力開始轉換成間葉細胞 (mesenchyme)型態，進行EMT 現象來助於腫瘤細胞惡化。由於過去有文獻指出GCIP 存在的細胞中會抑制其細胞週期調控蛋白cyclin D1的表現，我們也進一步證實GCIP 會藉由調節cyclin D1 promoter 的活性使得cyclin D1 表現量下降。另一方面，以暫時性轉染 (transient transfection)方式將GCIP 送入具有高度侵入 (invasive)及轉移 (metastatic)能力的後期乳癌細胞MDA-MB-435S 細胞中，同時我們也建立MDA-MB-435S 細胞的GCIP 穩定表現系統 (stable clone)。
結果我們發現vimentin 和N-Cadherin 這兩種和癌化呈現正相關的蛋白表現量有降低的趨勢，顯示EMT 現象的發生可能較為趨緩而有能力抑制腫瘤惡化。同時我們發
現有GCIP 表現的MDA-MB-435S 細胞移行以及侵入能力也有下降的情形。另外，我們也探討了GCIP 在MDA-MB-435S 細胞中基因表現靜默 (gene silencing)的情形應與甲基化 (DNA methylation)有關。在本實驗結果中，藉由了解P0 和GCIP 與EMT現象間的關係進一步確立二者在腫瘤惡化過程中扮演的角色；我們認為P0 和GCIP分別擁有促進及抑制乳癌癌化過程之能力。

Most cancer deaths are ascribed the failure treatment of migrating tumor cells.
Investigation of the mechanisms of tumor progression has become the major cynosure in cancer research. EMT (Epithelial-mesenchymal transition), the conversion of an epithelial cell to a mesenchymal cell was defined structural feature of organ development in embryogenesis, and its occurrence during tumor progression was demonstrated to be the major mechanism responsible for mediating invasiveness and metastasis of cancer cells nowadays. In our previous studies, the ribosomal protein P0, an essential component of the eukaryotic ribosomal stalk, was found to interact with the helix–loop–helix protein human Grap2 and cyclin D interacting protein (GCIP). Also, we found that overexpression of P0 in breast cancer and hepatocellular cancer cell lines promoted cell growth and colony formation. This increase of cell proliferating is apparently due to presence of increased level of free form P0 executed its tumorigenetic function by inhibiting GCIP-mediated reduction of Rb phosphorylation and enhancing the expression of cyclin D1. On the other hand, higher GCIP expression was observed in breast cancer patients with lower histological grade, mucinous carcinomas, and better clinical outcome during follow-up. Thus, our preliminary studies indicated P0 is a newly identified oncogenic protein and GCIP is a newly identified tumor suppressor of breast cancer cells.
In order to gain full understanding the mechanisms of tumor progression of P0 and GCIP, in this study, we first characterized the relationships between P0 and GCIP with EMT in human breast cancer cell. Our preliminary data of this study revealed that lower expression of EMT hallmark, E-Cadherin, was observed in a stable P0-overexpressing MCF-7, indicating that a significant correlation between high P0 and low E-Cadherin protein levels and higher expression of snail1 in breast cancer cell lines. Since a recent study reported that GCIP could inhibit the expression of cyclin D1, a key molecule involved in cell cycle and tumorigenesis in hepatocellular cancer cell, we investigate whether GCIP could inhibit cyclin D1 expression through the transcriptional repression of cyclin D1 promoter. To further confirm that GCIP is tumor suppressor, GCIP was transient transfected and stable expressed in malignant MDA-MB-435S. The stable GCIP-overexpression in MDA-MB-435S cell downregulated the expression of mesenchymal markers vimentin and N-Cadherin, suggesting a significant correlation of between high GCIP and low vimentin and N-Cadherin protein levels as well.
Furthermore, we also found that decreased the cell proliferation rate, migration capacity and invasion capability of the stable GCIP- overexpressing MDA-MB-435S. The investigation whether GCIP is inactivated by DNA methylation in malignant breast cancer cell is undertaken. In conclusion, we suggested that P0 promotes tumorigenesis and GCIP plays a tumor suppressor in breast cancer furthermore could provide the information for the diagnosis/prognosis and future target of antimetastasis therapy in breast cancer patients.

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